1. Field of the Invention
The present invention relates to novel polymeric compositions produced by co-grafting ungrafted polymeric blends and to toughened polyamide and material containing such tougheners.
2. Description of Related Art
There is considerable prior art concerned with improving the impact strength of polyamides. See for example, British Pat. No. 998,439 or Epstein, U.S. Pat. No. 4,174,358. See also Nylon Plastics, E. I. Kohan (1973, p. 346).
Improvement of impact strength of polyamide resins has long been of interest, for resistance to shattering or brittle breaking on impact of polyamide molded articles is a desirable feature of any molded article. By "ductile" is meant that cracks do not tend to propagate from the area of impact, and thus a resin having good ductility is one that is resistant to crack propagation caused by impact. The ductility of an article can also be measured by notched Izod test ASTM D-256-73.
A variety of additives have been added heretofore to polyamide resins to improve strength and ductility. For example, Epstein U.S. Pat. No. '358 describes improving impact strength and ductility by adding a selected random copolymer which reacts with the polyamide. However, the tendency of polyamides in general to break on impact in a brittle fashion increases as temperatures are lowered. Thus the use of molded articles for low temperature applications, such as winter sports equipment, automobile bumpers, and the like, is decreased.
U.S. Pat. No. 5,346,963 generally discloses the grafting of certain metallocene produced substantially linear ethylene polymers and discloses blends of this grafted material with either grafted or ungrafted thermoplastic polymers including HDPE, LDPE, LLDPE, ULDPE, polypropylene, EPDM and a host of other polymers. There is no teaching, however, of a composition or blend produced from co-grafting a blend of metallocene substantially linear ethylene polymers and either metallocene or non-metallocene produced polymers or copolymers such as polyethylene. Minor levels of polyethylene are sometimes used as excipients or additives in pre-graft polymers.
The present invention is an improvement over the compositions disclosed in the Epstein patent and subsequent nylon toughener patents, in that it has been found that certain polyamides, when toughened with certain compositions as claimed herein which have been prepared from cografting blends of copolymers of ethylene with one or more .alpha.-olefins having at least 4 carbon atoms and polymers having a tendency to mass ("massing polymers") such as EPDM or EPR (metallocene or otherwise) or other polymers which mass or agglomerate with grafting agents known in the art yield fabricated parts made from such blends having high impact resistance as well as other beneficial physical properties. Applicants believe the "co-graft" of this blend of ethylene-.alpha.-olefin and "massing polymers" is separate and distinct from a simple blend or mixture of grafted ethylene-.alpha.-olefin and grafted massing polymers.
In addition, the present inventors have discovered a process which is a significant improvement over the processes for making modified polymeric compositions and nylon toughened materials containing such compositions which relates to elimination of a partitioning agent such as polyethylene dust which has heretofore been necessary to eliminate massing. In particular, carboxylic acid or anhydride modified EPDM and EPR are commonly used as tougheners for polyamide. However due to the tacky nature of non-metallocene EPDM and EPR or any metallocene or non-metallocene polymer which has amorphous or tacky properties, pellets of these unmodified or acid or anhydride modified polymers are generally coated with a small amount (up to 10 wt %) of a partitioning agent, such as talc, carbon black or PE dust to make them free flowing. The addition of the partition agent is generally a costly and cumbersome step. This means an extra step in the modification process. Extra equipment is required to introduce the partitioning agent. Further, the quality of the modified polymer may suffer due to either too much or too little of the partitioning agent. Too little partitioning agent may result in massing of the product creating handling difficulties in the nylon compounding step. Too much powder may have a detrimental effect on the performance of the product as toughener for nylon. Even if applied in the appropriate amount, the partitioning agent may segregate during shipping, rendering it ineffective.
Thus, the present inventors have found a way of eliminating the need to add a partitioning agent to either pre-modified or modified EPDM or EPR or other modified massing polymer in the modification process while surprisingly retaining the excellent performance of the product as toughener for polyamide.
As discussed above, the use of modified EPDM or EPR as the toughening agent for polyamide is well known, see for example, Epstein (U.S. Pat. No. 4,174,358, Nov. 13, 1979). This and subsequent art which uses EPDM or EPR is characterized by the need to use a partitioning agent or to select an EPDM or EPR with increased crystallinity which does not have a tendency to mass.
By using a blend of a copolymer of ethylene and one or more .alpha.-olefins having at least 4 carbon atoms and an ethylene copolymer having a tendency to mass as a substrate in the inventors' improved process, it was found that a non-massing functional polymer is obtained. By suitably choosing the concentration of the copolymer of ethylene and one or more .alpha.-olefins having at least 4 carbon atoms, the density of this component and the graft level of the resulting polymer blend as described herein, the product can be used as a toughener for polyamide.